This research will describe the synaptic input to parasol ganglion cells in the primate retina. These cells provide the major input to the magnocellular layers of the lateral geniculate nucleus, which in turn provide input to cortical areas that mediate the perception of movement in the visual field. Peripheral parasol cells receive 80% of their input from amacrine cells and the remainder from bipolar cells, but the specific types of presynaptic amacrine cells and bipolar cells are not known. My working hypothesis is that two subtypes of diffuse bipolar cell provide the primary input, one to each of the two subtypes of parasol cells. I will also test the hypothesis that two kinds of narrowly- stratifying, wide-field amacrine cells receive input from the same bipolar cells and also make synapses onto parasol cells. First, tissue containing intracellularly-injected parasol cells will be immunolabelled and analyzed using a confocal microscope to determine whether various types of bipolar cells and amacrine cells make appositions onto their dendrites. Neurons that appear to be presynaptic to parasol cells will then be studied in the electron microscope to determine whether the close appositions seen at the light microscopic level represent areas of synaptic contact. One approach to identifying the presynaptic cells will be to reconstruct serial tangential sections through the injected parasol cell dendrites, and the other will be to modify the double-labelling techniques for electron microscopy.